THE JOURNAL OF
MARINE EDUCATION
Volume 21 • Number 4 • 2005
CORALS
THAT
BY FAN TSAO
AND
L IVE
ON
M OUNTAINTOPS
LANCE E. MORGAN
IN RECENT YEARS, scientists, with backing from the National Oceanic and Atmospheric Administration’s
(NOAA’s) Office of Ocean Exploration (OE) program, have begun to investigate underwater mountains
called seamounts. A variety of diverse deep-sea corals have been discovered living at great depths. Despite
this wave of exploration, only a small fraction of seamounts have been visited by scientists, though it is
likely that most shallow seamounts (those with summits less than 1,000 m below the ocean surface) have
already been commercially fished.
Numerous extinct and active volcanoes stand thousands
of meters tall on the seafloor in U.S. waters. From New
England to Alaska, scientists dive beneath the sea to explore
seamounts, often finding diverse communities of deep-sea
corals growing on the summits and slopes of these undersea
mountains. Living with these deep-sea corals are fishes
and invertebrates deriving benefits from the corals’ threedimensional structures.
A seamount is defined as an underwater mountain rising
more than 1,000 m above the surrounding seafloor. Deepsea corals live on seamounts because underwater currents
flow faster above seamounts, sweeping away sediment and
revealing rocky outcrops for the corals to settle and grow on
(Stone et al., 2004), and delivering food particles for deep-sea
corals to eat. Because rocky seafloor is rare and productivity
is limited in the deep sea, seamounts are an ideal place for
filter-feeding animals like deep-sea corals to live (Genin et
al., 1986). The distribution of deep-sea corals on seamounts
also suggests the importance of water currents. Deep-sea
corals tend to concentrate on the tops of sharply peaked
seamounts as opposed to the slopes, but on seamounts
with flat tops, corals reside along the perimeter of the flat
top–in both cases, where currents are the strongest (Genin
et al., 1986; De Vogeleare et al., 2005). Currents may carry
more coral larvae to seamounts allowing greater colonization
of seamounts than of the surrounding seafloor (Genin et al.,
1986). In addition, under certain environmental conditions,
currents above seamounts can develop into a gyre, or circular
eddy, that traps larvae and prevents them from drifting away
from the seamount.
Because of these unique characteristics and the rarity of
seamounts in the deep sea, many have very high levels of
endemism (species unique to one area of the world). In one
study of seamounts located in the Tasman and Coral Seas,
researchers found 850 new species (Richer de Forges et al.,
2000): 42 percent more than were discovered in the past
125 years of seamount research combined. Moreover, 34
percent of these species were potential endemics. Another
study determined that 16 to 33 percent of the 300 fish
and invertebrate species found on seamounts south of
Tasmania were restricted to seamount environments (Koslow
et al., 2000). Commercially valuable fishes aggregate around
seamounts (e.g., orange roughy [Hoplostethus atlanticus] and
pelagic armorhead [Pseudopentaceros wheeleri]), but their
low productivities and long life histories make them incredibly
vulnerable to overfishing, and the type of fishing gear used–
bottom trawls–results in damage to delicate structures such
as deep-sea corals (Morato et al., 2004; Koslow et al., 2001).
Many other species, including pelagic fishes, seabirds, and
marine mammals, often concentrate above seamounts.
Below we highlight some of the recent explorations of
seamounts off the east and west coasts of the U.S. and in the
Gulf of Alaska and Hawaii that have yielded exciting discoveries
of deep-sea coral communities and a better understanding of
the close relationship between corals and seamounts.
NEW ENGLAND SEAMOUNT CHAIN
The 1,500 km long New England Seamount Chain consists
of extinct volcanoes stretching form offshore Cape Cod to
halfway across the western Atlantic. The bases of these
seamounts are 5,000 m deep, but their tops reach depths
of 1,500 m. Recent research cruises revealed an astonishing
diversity of life on these unique seamount habitats and a high
abundance of deep-sea corals. In 2003, researchers onboard
the deep-diving submersible Alvin photographed and collected
seamount fauna on Bear, Kelvin, and Manning Seamounts. In
2004, scientists used remotely operated vehicles (ROVs)
equipped with robotic claws to survey the same seamounts in
addition to Balanus and Retriever Seamounts. The ROVs took
thousands of high-resolution digital images (Figure 1), and the
claws collected boxes of selected specimens. They also brought
to the surface some fossil corals for climate researchers to
study. Scientists reported 24 coral species between the depths
of 2,200 and 1,100 m, including ubiquitous bubblegum
DEEP-SEA CORALS
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THE JOURNAL OF
MARINE EDUCATION
Volume 21 • Number 4 • 2005
stars, and shrimps are common associates of the corals.
Certain species are found only on corals and nowhere else on
the seabed, such as the galatheid crab (Gastroptychus iaspus)
and the unbranched basket star (Asteronyx spp.). Species
assemblages in coral habitat vary with depth, but researchers
suspect these species associate with corals for three reasons:
1) suspension feeders climb on corals to elevate themselves
off the seafloor for faster current flow, which carries more
food; 2) small crustaceans use coral structures as refuge from
predators; and 3) some species such as sea stars and sea
spiders feed on corals directly.
Figure 1. This stunning yellow Enallopsammia stony coral with pink
Candidella is teeming with brittle stars on Manning Seamount. Image taken
by researchers on the NOAA “Mountains in the Sea 2004” cruise.
corals (Paragorgia spp.) and two-meter tall whip corals
(Lepidisis spp.). Balanus Seamount, explored in 2004, has
a forest of whip corals reaching heights of four meters. Fish
eggs, from a not yet identified species, were attached to
Metallorgorgia branches, indicating that deep-sea corals may
be important nursery grounds for fish. Marine biologists also
found bioluminescent bamboo corals (Keratoisis spp.) that
emitted blue-green light when disturbed.
DAVIDSON SEAMOUNT
Davidson Seamount is a massive seamount 120 km southwest
of Monterey, California. Its large base occupies a 40 km by 10
km area at a depth of 3,650 m. The 2,400 m tall seamount
is marked by dense ridges. In 2002, scientists conducted
90 hours of surveys on the seamount over the course of
six ROV dives. Deep-sea corals were distributed from almost
3,000 m deep to the seamount top. Deep-sea coral forests
were concentrated on the high-relief ridges near the top,
where bubblegum corals grow to two meters tall and two
meters wide. This cruise also observed soft mushroom corals
(Anthomastus spp.), black corals (Antipatharia spp.), and pink
corals (Corallium spp.). Almost all of the corals had associated
fauna, ranging from polycheate worms, basket stars, octopuses,
to thornyhead fish (De Vogeleare et al., 2005).
GULF OF ALASKA SEAMOUNTS
The 2004 Gulf of Alaska research cruise visited five seamounts
in the Kodiak-Bowie Seamount Chain with 18 submersible
dives down to a depth of 2,700 m. Like other seamount
cruises, this one revealed deep-sea coral species new
to science. Scientists found high levels of deep-sea coral
diversity as well as a high diversity of associated fishes
and invertebrates. The most abundant corals are red-tree
(Primnoids), bubblegum, bamboo (Isidids), and black corals.
Beside collecting corals with the submersible’s arms and
visually documenting the coral habitats, scientists also used a
slurp gun to vacuum animals from the corals and bring them
to the surface in order to further analyze the composition of
the deep-sea coral ecosystem. They found that crabs, brittle
HAWAIIAN RIDGE - EMPEROR SEAMOUNTS
This chain of islands and seamounts extends some 6,000 km
from a submerged active volcano just southwest of the island
of Hawaii to the Aleutian Trench off Alaska. The Hawaiian
islands themselves are not seamounts—yet. But as they
subside into the north Pacific they will become seamounts
in coming millennia. Scientists have explored small sections
of this chain and found intriguing animals such as deep-sea
corals, including valuable precious corals belonging to three
families: gold coral (Parazoanthidae; Figure 2), red or pink
coral (Corallidae), and bamboo coral (Isididae). Another taxon,
black coral (Antipathidae), is collected at shallower depths and
polished into jewelry. Perhaps the most significant fact about
the Emperor Seamount chain is the history of exploitation of
fishes in this region prior to scientific discovery. The pelagic
armorhead fishery began in 1968 when Russian fishermen
began fishing the summits and upper slopes of seamounts
in the southern Emperor Seamounts. By 1975, the combined
Russian and Japanese catch totaled approximately one million
tons of fish. In 1978, the U.S. began regulating this fishery on
the Hancock Seamounts, which are within the U.S. EEZ in the
northernmost section of the Northwestern Hawaiian Islands.
However, management was too late in coming, and in 1986, a
fishing moratorium was put in place after the fishery collapsed.
In 2004, even after an 18-year moratorium, fish populations
show no evidence of recovering.
There are an estimated 15,000 to 100,000 seamounts in the
world, yet only a small percentage have been explored. There
is reason to believe that more wonders of the deep sea are
waiting to be discovered, but these ecosystems are fragile and
under growing threat from bottom-trawl fishing. Conservation
organizations are currently advocating at the United Nations
for a moratorium on high-seas bottom trawling to protect
seamounts, but as yet there is little or no protection in
international waters for these unique ecosystems and species.
In the U.S., Davidson Seamount was set aside from trawling
recently, and some protection from bottom fishing has been
accorded the Gulf of Alaska Seamounts by the North Pacific
Fishery Management Council. These are laudable steps to
protect seamounts and to conserve the deep-sea corals and
other species that inhabit these places.
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Macrofauna off Southern Tasmania: Community Structure
and Impacts of Trawling.” Marine Ecology Progress Series
213: 111-125
Morato, T., W.L. Cheung, and T.J. Pitcher (2004). “Vulnerability
of Seamount Fish to Fishing: Fuzzy Analysis of LifeHistory Attributes.” pp. 51-60. Seamounts: Biodiversity and
Fisheries. T. Morato and D. Pauly (Eds.). Fisheries Centre of
the University of British Columbia, Vancover, Canada.
Richer de Forges, B., J.A. Koslow, and G.C.B. Poore (2000).
“Diversity and Endemism of the Benthic Seamount Fauna in
the Southwest Pacific.” Nature 405: 944-947
Figure 2. A large galathaeid crab on gold coral on Cross Seamount in
Hawaii. Image taken by researchers on the NOAA “Deep-Sea Precious
Corals” cruise in 2004.
FAN TSAO is Conservation Scientist at Marine Conservation
Biology Institute (MCBI). She received her master’s degree in
Marine Affairs from the University of Washington, where she
studied the natural and social sciences pertaining to marine
conservation.
LANCE E. MORGAN, PH.D.
is Chief Scientist for Marine
Conservation Biology Institute (MCBI).
REFERENCES
DeVogelaere, A.P., E.J. Burton, T. Trejo, C.E. King, D.A. Clague,
M.N. Tamburri, G.M. Cailliet, R.E. Kochevar, and W.J. Douros
(2005). “Deep-Sea Corals and Resource Protection at the
Davidson Seamount, California, U.S.A.” pp. 1189-1198.
Cold-Water Corals and Ecosystems. Andre Freiwald and J.
Murray Roberts (Eds.). Springer, Berlin.
Genin, A., P.K. Dayton, P. Lonsdale, and F. Spiess (1986).
“Corals on Seamount Peaks Provide Evidence of Current
Acceleration over Deep-Sea Topography.” Nature 322:
59-61
Stone, G.S., L.P. Madin, K. Stocks, G. Hovermale, P. Hoagland,
M. Schumacher, P. Etnoyer, C. Sotka, and H. Tausig (2004).
“Seamount Biodiversity, Exploitation and Conservation.” pp.
41-70 in L.K. Glover and S.A. Earle, eds. Defying Ocean’s
End: An Agenda for Action. Island Press, Washington, DC.
FOR MORE RESOURCES:
Seamounts Online:
http://seamounts.sdsc.edu/
Davidson Seamount:
http://oceanexplorer.noaa.gov/explorations/
02davidson/davidson.html
Gulf of Alaska Seamounts:
http://oceanexplorer.noaa.gov/explorations/04alaska/
welcome.html
New England Seamounts:
http://oceanexplorer.noaa.gov/explorations/
04mountains/welcome.html
Northwestern Hawaiian Island Seamounts:
http://oceanexplorer.noaa.gov/explorations/02hawaii/
welcome.html
Koslow, J.A., G.W. Boehlert, J.D.M. Gordon, R.L. Haedrich, P.
Lorance, and N. Parin (2000). “Continental Slope and DeepSea Fisheries: Implications for a Fragile Ecosystem.” Ices
Journal of Marine Science 57(3): 548-557
PHOTO CREDITS:
Koslow, J.A., K. Gowlett-Holmes, J.K. Lowry, T. O’Hara,
G.C.B. Poore, and A. Williams (2001). “Seamount Benthic
Page 11: Courtesy of Amy Baco-Taylor; Thomas Shirley; Pilots
T. Kerby and M. Cremer; and NOAA
Page 10: Courtesy of NOAA and Researchers on the
“Mountains in the Sea 2004” Cruise
Did You Know?
During the first year of the orange roughy fishery on South Tasman Rise seamounts off Australia, an estimated 1.6 tons of
coral were caught as bycatch by fisherman per hour of fishing, resulting in a total bycatch of 10,000 tons of coral that year.
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